by prachee rajput zoologist BHOPAL (IND)

1. Plant responses to
hormones & environmental
stimuli
 Responses include
– Developmental transitions
 Dormancy
 Germination
 Flowering
– Growth

2. Hormones & environmental
signals involve signal
transduction pathways

3. Internal and external signals

4. Hormones influence gene
expression
 Gene expression
regulated by
– microRNAs
– transcription factors

5. Plant hormones & growth
(abscisic acid)

8. Hormones interact to
promote/inhibit development

9. Auxins
tryptophan

10. Responses involving auxin
 Phototropism
 Gravitropism
 Cellular elongation
 Initiation of leaf primordia
 Apical dominance
 Root development
 Fruit development

11. Tropisms
 Permanent, directional growth
in response to an external
stimulus
– Positive tropisms
– Negative tropisms

12. Phototropism
 Stems are positively
phototropic
 How can plants grow towards
light?

14. Auxin and cell elongation
Acidified cell walls have increased elasticity

15. Phototropism research
Phototropin (NPH1)
and phototropism
-initiates a signal
transduction
pathway
-nph1 mutants
non-phototropic

17. Gravitropism

20. Gravitropism
How can it be demonstrated that
auxin is involved in gravitropism?

22. Gravitropism and root cap
amyloplasts
 Gravity regulated auxin transport, Ottenschlaumlger, Iris et al.
(2003) Proc. Natl. Acad. Sci. USA 100, 2987-2991

23. Auxin and initiation of
leaf primordia
 Pin mutant link

24. Responses involving auxin
 Apical dominance

25. Responses involving auxin
Formation of
adventitious
roots

26. Auxin produced by seeds
promotes ovary tissue
growth

27. Plant hormones
1. Are proteins encoded for by
genes
2. Act individually to bring about
changes in plant development
3. Function as receptors for
environmental signals
4. Both 1 and 3
5. None of these

28. Auxin
1. Prevents apical dominance
2. Is produced in shoot apical
meristems
3. Promotes seed development
inside fruit
4. All of these
5. None of these

29. Phototropin
1. Is a type of auxin
2. Promotes apical dominance
3. Is involved in stem growth
towards light
4. Is produced by seeds
5. All of these

30. Cytokinins – cell division and
differentiation

31. Cytokinin & tissue culture

32. From callus to somatic embryos

34. Gibberellins
Promotes:
• Germination
• Stem elongation
• Flowering
• Fruit development

35. Gibberellins
 Breaking dormancy
– Seed germination

36. Gibberellins
 Promotes cell
division &
elongation

38. Gibberellins
 Promotes
bolting in
biennials

39. Gibberellins
Promotes:
• Germination
• Stem elongation
• Flowering
• Fruit development

41. Gibberellin is part of a complex
signal transduction pathway
(see supplemental
reading, for related
information)

42.  Della proteins restrain growth
– GA and GID2 degrade Della proteins

43. Gibberellins and germination

44. Gibberellin promotes
vegetative growth

45. Abscisic acid
 Inhibits growth
 Promotes dormancy
 Closes stomata

46. Abscisic acid – inhibits
germination
– Promotes dormancy
– Leached by imbibition

47. ABA and stomatal
closure

48. ABA delays
flowering
 FCA – an RNA
binding protein
 FY – an mRNA
processing factor
 Flowering Locus C –
a flowering
repressor

49. Ethylene (CH2=CH2)
 Fruit ripening (promotes)
 Flowering (inhibits)
 Abscission (promotes)
 Sex expression in monoecious
species (ratio of ♀ to ♂)
 Thigmomorphogenesis (reduced
stem elongation in some
environments)

51. Thigmomorphogenesis

52. Brassinosteroids (BRs)
 60 types, brassinolide most common
 Stimulates cell elongation, leaf
expansion
 BR mutants – extreme dwarfs, small
crinkled leaves
– Dark grown BR mutants – de-etiolated

53. Plant Genes on Steroids
Science, Vol 307, Issue 5715, 1569-1570 , 11 March 2005
BIN2 catalyzes breakdown of BES1 & BZR2 proteins (phosphorylation)
BR regulates activity of key growth transcription factors
-BES1(activator)
-BZR1(repressor)

54. Figure 13.12 (p.290)

55. Figure 13.12 (p.290)

56. Plant Genes on Steroids
Science, Vol 307, Issue 5715, 1569-1570 , 11 March 2005
BIN2 catalyzes breakdown of BES1 & BZR2 proteins (phosphorylation)
BR regulates activity of key growth transcription factors
-BES1(activator)
-BZR1(repressor)

57. Responses to
environmental stimuli:
light
 Phototropism
 Stomata opening
 Stem elongation
 Photodormancy
(photoblastism)
 Photoperiodism

58. Phytochrome
 Phytochromes are proteins
with a light absorbing pigment
attached (chromophore)
– Mediates stem elongation, seed
germination, timing of flowering

60. Phytochrome
structure

61. Two forms of
phytochrome

62. Phytochrome & stem growth
•Etiolation
occurs in low
light or dark …
why?
•Does Pfr
inhibit or
promote stem
elongation?
Phytochrome and hormonal control of stem elongation

63. Phytochrome and
seed germination
 Photodormancy & photoblastic
seeds
– Germination activated by light
 Some plants, by red light
 Some plants, by far-red light
Negative photoblastism (tomato),
Pfr inhibits germination
Positive photoblastism (lettuce),
Pfr promotes germination

64. Lettuce is positively photoblastic
 30-60% lettuce seed germinate in dark
 85-95% lettuce seed germinate in light

65. Phytochrome,
photoperiodism & flowering

67. Manipulation of
photoperiod
 Poinsettia
industry
 Chrysanthemums
 Why won’t my
Christmas cactus
bloom?

68. Brassinosteroids
1. Promote seed germination in
response to light
2. Promotes flowering in response to
day length
3. Are proteins with an attached
light absorbing chromophore
4. Regulate transcription factors
involved in growth
5. All of these

69. Which of the following is
true of phytochrome?
1. Pfr absorbs red light and Pr absorbs
far red light
2. Pr is the active form of
phytochrome and Pfr is the inactive
form of phytochrome
3. Pfr promotes germination in seeds
requiring light
4. All of these
5. None of these

70. Photoperiodism
1. Determines seed
dormancy/germination in response
to light/dark
2. Determines flowering in response
to day length
3. Is a protein with an attached light
absorbing chromophore
4. Controls stem growth in response
to light/dark
5. All of these

71. Circadian rhythms –
sleep movements
(nyctinasty)

72. Nyctinasty

74. Solar tracking
(heliotropism)

75. Response to
mechanical stimuli
(seismonasty)

76. Seismonasty – Mimosa pudica

77. Seismonasty

78. Seismonasty
 Venus flytrap

79. Response to
environmental stimuli:
Induced resistance
 Herbivore attack, systemin
(18aa polypeptide hormone) &
jasmonic acid (1-alpha, 2-beta-3-oxo-2-(cis-
2-pentenyl)-cyclopentane acetic acid)

80. Figure 1 Model for the activation of
defense genes in tomato in response
to wounding and insect attack. After
wounding, systemin is released from
its precursor prosystemin by
proteolytic processing. Systemin
subsequently binds a membrane-
bound receptor to initiate an
intracellular signaling cascade,
including the activities of a MAP
kinase, a phospholipase, a calcium
dependent protein kinase, an
extracellular alkalinization, and the
release of linlenic acid from
membranes. Linolenic acid is
converted to jasmonic acid, a
messenger for early defense gene
activation. Catalytic activity of
polygalaturonase, an early gene,
leads to generation of hydrogen
peroxide acting as a second
messenger for late gene activation. R,
receptor; MAPK, MAP kinase;
Ca2+
PK; calcium dependent protein
kinase; PLA2
, phospholipase A2
; LA,
linolenic acid; JA, jasmonic acid; pm,
plasma membrane.
 H2O2 prevents cell wall digestion by fungal pectinases

81. Response to
environmental stimuli:
Induced resistance
 Pathogens & the
hypersensitive response (HR)

82. HR response & systemic
acquired resistance (SAR)

83. SAR responses
 Lignification of cell walls
 Antimicrobial molecules
– PR-proteins (pathogen related
proteins)
– Chitinases
– Phytoalexins (inhibit protein
synthesis

84. SAR model